This invention relates to metal modified phenolic resins for use in carbonless copying and record systems.
Carbonless copying and record systems include thermal paper and pressure sensitive paper. Thermal paper and pressure sensitive paper copying systems each utilize a color developer and a color precursor as components which are coated onto the paper.
In the thermal paper system, legible colored images are developed through a chemical reaction between the color developer and the color precursor. This reaction is initiated by the localized application of heat from the printing head of a thermal printer, which causes the components to fuse and form the print.
Thermal papers are used in data processing terminals, calculators, chart and facsimile recording devices, electrocardiographs, and various non-impact printing units.
In pressure sensitive paper systems, the color precursor, also referred to as chromogenic material, is generally in the form of microscopic capsules, which are coated onto the paper.
This coating is referred to as the "CB coating." The paper with the CB coating is then placed in contact with a supporting sheet of paper whose surface is coated with one or more color developers. The color developer coating is referred to as the "CF coating."
The CB and CF coatings are generally colorless and remain so until sufficient pressure is brought upon the superimposed CB and CF coatings as with a typewriter. This causes the encapsulated color precursors to rupture from the CB coating and transfer to the CF coating whereupon reaction occurs with the color developer to form an image restricted along the lines wherein the pressure was applied.
Another type of pressure sensitive paper, referred to as "self-contained paper" contains an imaging system in a single coating that is applied to only one side of the paper. The single coating contains both the color precursor, again generally in encapsulated form, and the color developer. The application of pressure to the surface of the paper, as with a typewriter or other writing instrument, causes the rupture of the color precursor capsule and its reaction with the surrounding color developer to form an image.
U.S. Pat. Nos. 3,539,375 and 3,293,055 both to Baum, and U.S. Pat. Nos. 3,895,173 and 3,843,384 both to Adachi et al are related to thermal paper systems.
U.S. Pat. No. 2,712,507 to Green and U.S. Pat. No. 3,672,935 to Miller et al relate to pressure sensitive copying systems. U.S. Pat. No. 2,730,457 to Green and U.S. Pat. No. 4,197,346 to Stevens et al relate to self-contained pressure sensitive systems.
Phenol-aldehyde (novolak) resins are widely used as color developers in carbonless paper copying systems. See U.S. Pat. No. 3,455,721 to Phillips et al; U.S. Pat. No. 3,466,184 to Bowler et al; U.S. Pat. No. 3,672,935 to Miller et al and U.S. Pat. No. 4,166,664 to Kay et al.
It is also known to use metal compounds to enhance the color forming reaction of phenolic resins with chromogens. U.S. Pat. No. 3,516,845 to Brockett discloses acidic water soluble metal salts incorporated in aqueous coatings of ground novolak resins. U.S. Pat. No. 3,723,156 to Brockett et al discloses a similar use of oil soluble metal salts. U.S. Pat. No. 3,732,120 to Brockett et al and U.S. Pat. No. 3,737,410 to Mueller disclose the interaction of a metal compound such as zinc hydroxy-benzoate, zinc acetylacetonate and zinc dibenzoate with a para-substituted novolak resin by melting the resin and metal compound together to give a color developer which shows increased color intensity and resistance to fading.
U.S. Pat. No. 4,173,684 to Stolfo discloses metal modified novolak resins containing salicylic acid formed by combining one or more para-substituted phenols and salicylic acid by condensation in the presence of an acid catalyst with formaldehyde. The novolak resins are then metal modified by melting with a metal salt.
U.S. Pat. No. 3,732,120 to Brockett et al discloses that the effectiveness of metal-modified resins in enhancing color production in chromogenic dye precursors such as crystal violet lactone (CVL), is inversely related to the chelating-ability of the metal ion used to make the metal modified resin.
U.S. Pat. No. 4,173,684 to Stolfo and U.S. Pat. No. 3,732,120 to Brockett et al disclose the formation of metal modified novolak resins in a two-stage process. The first stage involves the formation of the resin, followed by the metal modification of the resin, or chelation step.